My main question would be this: When you say "like Monster.com" what exactly are you referring to? What is your secret sauce?

As Lee mentioned, if there is a specific filtering/matching algorithm that you've developed that you feel fits the following categories (requirements for a patent) then the answer is YES, you should file for a utility patent.

1) New and useful (No one else has Known about or used this process or algorithm in the US & there are NO patents on this anywhere in the world)
2) Utility (actually useful in real life or a very solid theoretical foundation for being useful)
3) Novel (Unique, authentic idea - See #1)
4) Non-obvious (This is the hardest obstacle to get through. Simply put, your idea can't just be the combination of 2 other patented Ideas. Previous patents are called "prior art" and your idea will be compared against prior art to ensure there was a substantial difference in your invention versus previous inventions. Patent examiners will also look at the commercial marketplace.
5) You Haven't publicly disclosed your idea

If you don't have a secret sauce and you're creating a website that duplicates someone else's algorithm/process then you may be infringing on someone else's patent & you should ask yourself why you're going into business in the first place.